Our long term objective is to understand the maintenance of upper airway patency in health and disease. the proposed studies are designed to provide better insight into mechanisms that are poorly understood at present. Special emphasis is given to neuroregulation of upper airway muscles Stimulation of laryngeal afferent is known to alter the activity of various upper airway muscles. Anesthetized, spontaneously breathing dogs and rabbits will be used in the animal studies. Action potentials from single fibers of the superior laryngeal nerve will be monitored from its peripheral cut end. Electromyograms of posterior cricoarytenoid, genioglossus and al ae nasi muscles will be recorded with bipolar wire electrodes. Behavior of laryngeal mechanoreceptors and the response of upper airway muscles during upper airway occlusion will be documented before and after paralysis of intrinsic laryngeal muscles (by cold block of recurrent laryngeal nerves). The role of volume-related feedback from the lungs on the response to upper airway pressure will be tested by blocking the activity of slowly adapting receptors with SO2 in anesthestized rabbits. The effects of cooling of the laryngeal mucosa on the mechanoreceptor response to pressure changes will be evaluated, and single fiber action potential recorded during upper airway occlusion. In separate experiments the effect on tracheal smooth muscle activity will also be studied by monitoring smooth muscle tone in the extra-thoracic trachea. The hypothesis that laryngeal cooling is responsible for the respiratory inhibition observed in newborn animals during airflow through the upper airway will be tested by comparing the responses at different laryngeal temperatures at constant flow rate. Finally, in human studies, we plan to identify the factors responsible for the alteration of breathing pattern during feeding of expressed milk and formula. In addition, the rate of milk flow will be altered using high and low flow rate nipples. The proposed studies are anticipated to provide valuable insights into airway maintenance and regulation of breathing in health and disease, especially in sleep apnea and cold-induced bronchospasm.